PROTOPLASMIC STREAMING IN RELATION TO GEL 

 STRUCTURE IN THE CYTOPLASM 



Douglas A. Marsland 

 Washington Square College of Arts and Science, New York University 



I. INTRODUCTION 



Reversible sol-gel transformations are commonly recognized in 

 protoplasmic systems, and for some time it has been thought that 

 these reactions may play an important role in physiological activity. 

 Thus Mast ('26 and '31), and Lewis ('39) have considered that the 

 movement of amoeboid cells depends upon a series of gelations 

 occurring at the anterior ends of the pseudopodia, and upon com- 

 pensating processes of solation in the posterior part of the cell. Aside 

 from this case, however, examples establishing the physiological 

 importance of sol-gel reactions have not been demonstrated very 

 clearly. 



A. SOL-GEL EQUILIBRIA IN RELATION TO HYDROSTATIC PRESSURE 



A relationship between hydrostatic pressure and the structural 

 characteristics of protoplasmic gels was first revealed by Dugald 

 E. S. Brown in 1934. Brown ('34c) found that the central mass of 

 the protoplasm of the Arbacia egg is relatively fluid compared to a 

 cortical layer, about 5 microns thick, which displays the properties 

 of a fairly rigid gel. When these eggs were centrifuged at atmos- 

 pheric pressure in a weak centrifugal field, the granular components 

 of the central fluid protoplasm were readily displaced, but the gran- 

 ules of the gelated cortex, mainly the pigment granules, remained 

 quite fixed. But when the centrifuging was done at increasingly 

 higher hydrostatic pressure, up to 10,000 pounds per square inch, 

 the cortical gel displayed a greater and greater degree of lique- 

 faction. In the higher range of pressure the pigment granules were 

 displaced with great rapidity, and at 10,000 lbs. /in.,- the cortical 

 gel offered less than 10 per cent of its atmospheric resistance. 



Subsequent work has demonstrated that hydrostatic pressure 

 imposes solation upon the protoplasmic gels of animal and plant cells 

 generally. Among the animals, the effect has been shown in a num- 

 ber of different eggs;^ in two kinds of amoeba,- in the tentacles of 



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